The subject invention generally concerns test and measurement instruments, and in particular concerns those test and measurement instruments employing telecom mask features.
In the telecommunications industry, it is commonplace to perform a test to determine if a particular signal is in compliance with parameters established by national and international communications standards bodies such as ITU-T and ANSI. A primary way to perform such a compliance test is to compare the pulse shape of a waveform acquired by an oscilloscope to a waveform xe2x80x9cmaskxe2x80x9d. The mask defines a pathway having minimum and maximum amplitude values, predetermined bit rate, and defined minimum slope on signal edges (i.e., minimum bandwidth). If the signal under test stays within the pathway boundaries, then the signal passes the test. This kind of test is known as Telecom Mask Testing.
A recent innovation in oscilloscope features has been a xe2x80x9cAUTOSET TO MASKxe2x80x9d function. The AUTOSET TO MASK function automatically sets up the horizontal, vertical, and triggering settings on the oscilloscope to accommodate the expected signal, and overlays a mask on the oscilloscope display. The procedure followed in the operation of an AUTOSET TO MASK function is to set the horizontal and vertical scales to a nominal value, acquire a waveform, and adjust the scale and position of the waveform by adjusting the settings of the input A/D converters, and display the mask.
After an AUTOSET TO MASK function sets up the acquired waveform and displays the mask, the telecom mask testing software checks for intrusions into the mask area by the waveform being tested (i.e., violations, or mask hits) that would indicate that the waveform does not comply with applicable telecommunications standards.
In the telecommunications industry, it has been observed that higher core and access data rates require higher capacity line cards, also known as network interface cards. Such high capacity line cards can down convert an STMIE signal (156 Mbits per second) to 63 channels of E1 signals (2 Mbits per second). As multi-channel devices are designed into networkinterface cards, the need for high-speed pass/fail testing of multiple channels becomes critical.
What is needed is a high-speed solution to the problem of testing telecom signals of multiple channels of telecommunications equipment for compliance with a telecommunications standard.
In a test and measurement instrument having M signal input channels, individual samples representing a signal from each channel are compared to mask pixels to detect noncompliance with a given specification. Initial mask and waveform positions on a display screen of the oscilloscope are determined by an AUTOSET TO MASK function. Comparison of mask pixels and waveform pixels to detect collision between a waveform pixel and a mask pixel (i.e., a mask violation) is performed substantially in real time, as the pixels are being composited into a raster memory by a rasterizer. Acquisitions are performed simultaneously and repeatedly. Acquired waveforms from all M signal input channels are sequentially compared to the mask and drawn on screen during the following acquisition period. Thus, M waveforms can be tested for compliance with a telecom mask substantially within a single acquisition time period. A system employing a multiplexer can select M channels at a time from a group of N channels to decrease the time required to test all N channels. The intensity of pixels representing samples violating the mask is preferably increased for better visibility against the telecom mask.